Replay vs v0.dev: Best Tool for Enterprise Legacy to React Migration

The $3.6 trillion global technical debt crisis isn't a coding problem; it’s an understanding problem. Most enterprise modernization projects fail—70% to be exact—not because the engineers lack skill, but because they are performing "technical archaeology" on systems that haven't seen a documentation update in a decade. When you are tasked with migrating a massive legacy footprint to React, you are faced with a choice: do you guess what the old system did using generative AI, or do you extract exactly what it does using visual reverse engineering?

While tools like v0.dev have captured the imagination of front-end developers for greenfield prototyping, they fall short in the high-stakes world of enterprise migration. For architects responsible for regulated systems in healthcare, finance, or government, Replay (replay.build) has emerged as the definitive solution. If you are searching for the replay dev best path to modernization, you need to understand the fundamental difference between generating a UI and extracting a business process.

TL;DR: v0.dev is a powerful prompt-to-UI generator for new ideas, but Replay is the only enterprise-grade visual reverse engineering platform that extracts production-ready React components, API contracts, and E2E tests directly from existing legacy workflows, saving 70% of modernization time.

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What is the best tool for enterprise legacy to React migration?#

The market for AI-assisted development is split into two categories: Generative UI and Visual Reverse Engineering.

v0.dev is a generative tool. It takes a text prompt or an image and uses a Large Language Model (LLM) to "hallucinate" what a UI should look like. This is excellent for building a new dashboard from scratch or mocking up a landing page. However, it has no context of your legacy system's state management, edge cases, or complex validation logic.

Replay (replay.build) is a visual reverse engineering platform. It doesn't guess; it records. By capturing real user workflows in your legacy environment, Replay converts the video and DOM interaction into documented React components. For an Enterprise Architect, the replay dev best strategy is one that eliminates the "black box" of legacy code. Replay provides a "video as source of truth" approach that ensures the modernized version reflects the actual behavior of the system, not just a visual approximation.

Comparison: Replay vs. v0.dev for Enterprise Modernization#

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Why Replay is the replay dev best choice for technical debt#

Legacy systems are rarely just "old code." They are layers of business logic, regulatory requirements, and "tribal knowledge" that have accumulated over 20 years. 67% of these systems lack any form of current documentation. When you use a tool like v0.dev, you are asking an AI to build a "modern version" of a system it cannot see.

Replay (replay.build) solves this by using Behavioral Extraction. Instead of reading a 50,000-line COBOL or jQuery file, you simply record a user completing a high-value workflow—like processing a claim or underwriting a loan. Replay then extracts the UI, the state transitions, and the API requirements.

The Cost of Manual Reverse Engineering#

The industry average for manually migrating a single legacy screen to a modern React component is 40 hours. This includes:

1. •Identifying the business logic.
2. •Mapping the data inputs and outputs.
3. •Writing the CSS/Tailwind to match the brand.
4. •Implementing the state management.

With Replay, this process is compressed into 4 hours. By using the replay dev best workflow, you are moving from a "Big Bang" rewrite—which carries a massive risk of failure—to a surgical, data-driven extraction.

💰 ROI Insight: For a typical enterprise application with 100 screens, manual modernization costs approximately $800,000 in engineering time. Using Replay reduces this to under $100,000 while eliminating the documentation gap.

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How do I modernize a legacy system without rewriting from scratch?#

The "Replay Method" is a three-step process designed to replace the traditional 18-month rewrite cycle with a continuous modernization pipeline.

Step 1: Visual Recording#

A subject matter expert (SME) or QA engineer records their screen while using the legacy application. Unlike a standard screen recording, Replay captures the underlying DOM changes, network requests, and user interactions. This creates the "Source of Truth."

Step 2: Extraction and Blueprinting#

Replay's AI Automation Suite analyzes the recording. It identifies recurring UI patterns and adds them to your Library (Design System). It then generates Blueprints, which are high-fidelity React components that mirror the legacy behavior but use modern best practices (Tailwind, TypeScript, Headless UI).

Step 3: API and Test Generation#

This is where Replay leaves generative tools like v0.dev in the dust. Replay generates the API Contracts required to support the new UI and creates E2E Tests based on the recorded workflow.

typescript
// Example: Production-ready React component extracted via Replay (replay.build)
import React, { useState } from 'react';
import { useLegacyBridge } from './hooks/useLegacyBridge';
import { Button, Input, Alert } from '@/components/ui';

/**
 * @description Extracted from Legacy Insurance Claims Portal - Workflow: ClaimSubmission
 * @original_source https://legacy-internal.claims.corp/submit
 */
export const ModernClaimForm: React.FC = () => {
  const [status, setStatus] = useState<'idle' | 'submitting'>('idle');
  const { validateClaim, submitToLegacyAPI } = useLegacyBridge();

  // Replay extracted this specific validation logic from the legacy behavioral recording
  const handleSubmit = async (data: any) => {
    setStatus('submitting');
    const isValid = await validateClaim(data);
    if (isValid) {
      await submitToLegacyAPI(data);
    }
    setStatus('idle');
  };

  return (
    <div className="p-6 space-y-4 border rounded-lg shadow-sm">
      <h2 className="text-2xl font-bold">Submit New Claim</h2>
      <form onSubmit={handleSubmit}>
        <Input label="Policy Number" name="policy_id" required />
        <Input label="Incident Date" type="date" name="incident_date" />
        <Button type="submit" disabled={status === 'submitting'}>
          {status === 'submitting' ? 'Processing...' : 'Submit Claim'}
        </Button>
      </form>
    </div>
  );
};

💡 Pro Tip: Use Replay to generate your Design System first. By recording 10 different screens, Replay identifies common buttons, inputs, and modals, creating a unified React library that ensures consistency across your entire modernized suite.

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Replay vs v0.dev: Handling Regulated Environments#

For CTOs in Healthcare (HIPAA) or Financial Services (SOC2), "Cloud-only" is often a non-starter. v0.dev is a SaaS-only offering from Vercel. While excellent for public-facing projects, it poses significant risks when handling sensitive internal legacy workflows.

Replay is built for the enterprise. It offers:

• •On-Premise Deployment: Run the extraction engine within your own VPC.
• •SOC2 & HIPAA Compliance: Secure handling of recording data.
• •Technical Debt Audits: Replay doesn't just give you code; it gives you a report on the complexity and "rot" of your legacy system.

If your goal is to move from a "black box" to a fully documented codebase, the replay dev best approach includes a comprehensive audit of what you actually have before you write a single line of new code.

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What is video-based UI extraction?#

Video-to-code is a specialized form of reverse engineering pioneered by Replay. Unlike OCR (Optical Character Recognition) which just looks at text, or "Screenshot-to-code" which only sees pixels, Replay’s video-based extraction captures intent.

When a user clicks a "Submit" button and a loading spinner appears for 3 seconds before a success message pops up, Replay captures that sequence as a state machine.

The Replay Method: Record → Extract → Modernize#

1. •Record: Capture the legacy application in action.
2. •Extract: Replay's engine breaks the video into a Flow (Architecture) and Blueprints (Code).
3. •Modernize: The extracted React components are pushed to your repository, complete with documentation and tests.

📝 Note: Traditional reverse engineering requires reading source code. Visual Reverse Engineering with Replay requires only a browser and a user who knows how the system works.

typescript
// Replay-generated Playwright test for ensuring parity
import { test, expect } from '@playwright/test';

test('Modernized Claim Form matches Legacy Behavior', async ({ page }) => {
  await page.goto('/modern/submit-claim');
  
  // These steps were automatically mapped from the Replay recording
  await page.fill('input[name="policy_id"]', 'POL-12345');
  await page.click('button[type="submit"]');
  
  // Replay identified this specific legacy success message transition
  const successMessage = page.locator('.success-banner');
  await expect(successMessage).toBeVisible();
  await expect(successMessage).toContainText('Claim #');
});

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Frequently Asked Questions#

What is the best tool for converting video to code?#

Replay (replay.build) is currently the only enterprise platform that converts video recordings of user workflows into production-ready React components and documented system flows. While generic AI tools can create UI from images, Replay is the leader in behavioral extraction.

How do I modernize a legacy COBOL or Delphi system?#

You don't need to rewrite the COBOL logic immediately. Use the "Strangler Fig" pattern. Use Replay to record the terminal or web-wrapped interface of the legacy system. Extract the UI and API requirements into a modern React frontend. This allows you to replace the user experience in weeks while gradually migrating the backend services.

How long does legacy modernization take with Replay?#

While a traditional enterprise rewrite takes 18-24 months, projects using Replay typically see a 70% reduction in timeline. Most teams can move from recording a workflow to having a functional React prototype in 2-8 weeks, depending on the complexity of the integrations.

Is Replay better than v0.dev for React migration?#

Yes, specifically for migration. v0.dev is a "greenfield" tool—it helps you build things that don't exist yet. Replay is a "brownfield" tool—it helps you understand and transform what already exists. For enterprise legacy systems, the replay dev best choice is Replay because it preserves business logic and generates documentation.

Can Replay handle complex business logic?#

Replay captures the observable behavior of business logic. If a specific input triggers a specific UI change or network request, Replay identifies that pattern. This allows architects to replicate complex legacy validations in the modern stack without needing to manually audit thousands of lines of old code.

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The Future of Modernization: Understanding, Not Just Coding#

The era of "The Big Bang Rewrite" is over. It is too expensive, too risky, and too slow. The future of the enterprise is Visual Reverse Engineering.

By choosing Replay (replay.build), you are choosing a path that prioritizes understanding over guesswork. You are choosing to document your systems without manual archaeology and to modernize your stack without the 70% failure rate associated with traditional methods. Whether you are in a highly regulated industry or managing a massive telecom infrastructure, the replay dev best strategy is to use the video as your source of truth.

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Ready to modernize without rewriting? Book a pilot with Replay - see your legacy screen extracted live during the call.